No. 3-] DEVELOPMENT OF MARIAE SPOiXGES. 337 



by an ectodermal membrane). The change of contour con- 

 cerns especially the parenchyma, which pushes out lobes and 

 processes inside the ectodermal membrane, thus acquiring 

 from time to time entirely different outlines, while the sur- 

 rounding ectodermal membrane remains practically unchanged. 

 If the parenchyma, however, continues to change its contour 

 in such a way that the shape of the whole sponge is altered, 

 as, for instance, in passing from a circular outline to a shape 

 such as that in Fig. 91, then the ectodermal membrane is 

 involved and its edge gradually altered so as to remain more 

 or less parallel with the general contour of the parenchyma. 



In sponges which have assumed elongated irregular shapes, 

 like that of Fig. 91, the change of contour sometimes leads 

 to the complete division of the body into two independent 

 sponges. This phenomenon I have twice observed. I thought 

 at one time that I had witnessed the converse phenomenon, 

 i.e. the fusion of two attached sponges into one. I observed 

 two sponges, a couple of days after attachment, which lay near 

 each other, grow nearer and nearer until after fifteen to twenty 

 hours they met and seemed to fuse into one body of an irreg- 

 ularly oval shape. Across this body, however, could be seen 

 the seam or line of fusion, and the union must have been one 

 of close juxtaposition only, for after a few hours the sponges 

 again separated along this line and afterwards remained inde- 

 pendent. Fusion of the swimming larvae, into a single large 

 one, as occasionally happens in the Coelenterates (Manicina) 

 I have never observed. 



Canal System. — The canals and subdermal cavities appear 

 as separate lacunae in the parenchyma, the surrounding cells 

 becoming modified into epithelioid membranes, Figs. 93 and 

 94, s. d. c., can. The separate lacunae subsequently become 

 united into a canal system, as in Esperella. The flagellated 

 chambers likewise originate as independent structures, which 

 later acquire connection with the canals, Fig. 93. The sub- 

 dermal cavities, which in some cases are very extensive, as in 

 Fig. 91, J. ^. c., are roofed over by a dermal membrane {d. mem. 

 in Fig. 93), quite like the same structure in the young Es- 

 perella. As in Esperella, no system is followed in regard to 



